1. Field of the Invention
The present invention relates generally to an OFDMA (Orthogonal Frequency Division Multiple Access) cellular communication system, and in particular, to a resource allocation method for an OFDMA cellular communication system.
2. Description of the Related Art
For future-generation mobile communications, high-speed, high-quality data transmission is required to support various multimedia services having a high quality. In order to provide these high quality services, active studies have recently been conducted on OFDMA.
OFDM (Orthogonal Frequency Division Multiplexing), the operation on which OFDMA is based, is used as a physical layer transmission scheme for diverse wireless communication systems including WLAN (Wireless Local Area Network), digital TV, and future-generation mobile communication systems because of its capability for high-speed communication on a frequency selective fading channel with a low equalization complexity.
IEEE 802.16 is one of the wideband wireless communication standards developed by IEEE work groups, and approved in December 2001. IEEE 802.16 is for fixed broadband wireless systems using a point-to-multipoint architecture, defining the use of bandwidth between the licensed 10 GHz and 66 GHz. Ratified in January 2003, an amendment to the IEEE 802.6, IEEE 802.16a provides a non-line-of-sight extension in bandwidth between 2 GHz and 11 GHz to support transmission at 700 Mbps within a range of up to 50 kilometers.
The IEEE 802.16 protocol defines a PHY (PHYsical) layer, a MAC (Medium Access Control) layer, and convergence sublayers (CS) for transport of IP (Internet Protocol), Ethernet, and ATM (Asynchronous Transfer Mode).
Many technologies are under discussion to support high data rates in OFDMA wireless communication systems including IEEE 802.16 systems. The majority of them are directed to dynamic frequency and power resource allocation mechanisms for subchannels or subcarriers. Resource allocation requires accurate channel information and notification of specific allocation information. The PHY standard of 4th generation mobile communication systems is directed to frequency hopping and a plurality of subcarriers. Therefore, transmission of a common dynamic resource allocation information message related to hundreds of subcarriers to all subscriber stations (SSs) causes serious control load in the systems. More specifically, on the downlink, frequency hopping is assumed on a per-OFDM symbol basis. Accordingly, as many pieces of resource allocation information as a power of the number of allocated time resources are required.
A radio frame defined in the IEEE 802.16 standard starts with a preamble for synchronization and downlink transmission, and is followed by control fields including downlink MAP (DL-MAP) and uplink MAP (UL-MAP) messages.
The DL-MAP message includes parameters such as PHY Synchronization, Base Station Identification (BS ID), Allocation Start Time, Number of Elements, and MAP Information Elements (MAP IEs). The DL-MAP IEs each include Downlink Interval Usage Code (DUIC) by which downlink transmission is defined. Meanwhile, the UL-MAP message provides the start time of each uplink transmission for the SS in the base station, together with Uplink Interval Usage Code (UIUC) for each burst. The IEEE 802.16d standard defines the DL-MAP IE in the following table.
TABLE 1DL-MAP Information Element ( ) {DIUC4bitsOFDMA Symbol Offset10bitsSubchannel Offset5bitsBoosting3bitsNo. OFDMA Symbols9bitsNo. Subchannels5}
In Table 1, the DL-MAP IE defines subchannels and OFDM symbols used for the PHY burst, and a related DIUC.
The DIUC represents a downlink interval usage code, the OFDMA Symbol Offset indicates the offset of the OFDM symbol in which the burst starts, and the Subchannel Offset indicates the lowest-index OFDM subchannel for carrying the burst. Boosting is an indicator indicating transmit power amplification, No. OFDMA Symbols indicates the number of OFDM symbols for carrying the downlink PHY burst, and No. Subchannels indicates the number of OFDMA subchannels of successive indexes used to carry the burst.
The above 4th generation mobile communication PHY standard considers frequency hopping and multiple subcarriers. Therefore, common transmission of a dynamic resource allocation information message about hundreds of subcarriers to all SSs causes serious control load in the system. Further, on the downlink, because frequency hopping is assumed on a per-OFDM symbol basis, as many pieces of allocation information as the power of the number of allocated time resources are required.
However, the existing IEEE 802.16d standard has limits in implementing optimum resource allocation because the DL-MAP IE defines an AMCS (Adaptive Modulation and Coding Scheme) on a burst basis.